Automatic recorder



3 Sheets-Sheet l %R W Rm v E Q i mzH i us mm Jan. 2, 1945. D. H. CAMERONAUTOMATIC RECORDER Filed March 27, 1957 Jan. 2, 1945. CAMERON 2,366,383

AUTOMATIC RECORDER Filed March 27 1957 5 Sheets-Sheet 2 @5 2. m ,lliiiliI F "102 wenz 13 ZmZdfl Qlmeroizz/ 7/1 a 4344441 f/z Q 1945- D. H.CAMERON AUTOMATIC RECORDER Filed March 27, 1957 3 Sheets-Sheet 3iii-1101482115) m m \NW Patented Jan. 2, 1945 AUTOMATIC RECORDERDonaidli. Cameron,

Win, assignor to Racine, B. D. Eisendrath Tanning 00., Chicago, 111., acorporation of Illinois Application March 27, 1837, Serial No. 133,333

Claims.

This invention relates to automatic recorders, and has for its principalobject to provide an improved recorder for automatically makingpermanent records of p y ical conditions.

While the invention may be embodied in recorders for various physicalconditions, it will be described herein in its specific application torecording hydrogen ion concentration. It is, however, clearly to beunderstood that the invention is not intended to be limited to itshydrogen ion application since it may be utilized to record any electriceiicct or any physical effect which can be transformed into an electricefiect.

The invention will be fully understood from the following description ofa preferred embodiment thereof, taken in conjunction with theaccompanying drawings, in which:

Figure 1 is a front elevation of a recorder embodying my invention,parts of the recorder being shown in section for the sake ofbetter-"illustration;

Fig. 2 is an end elevation of the recorder as viewed from the right inFig. 1;

Fig. 3 is a sectional elevation through my recorder, taken on the line3-3 of Fig. 1;

Fig. 4 is a sectional plan detail taken on the line 4-4 of Fig. 1; and

Fig. 5 is a wiring diagram.

Referring to the drawings, and particularly to Fig. 5, the referencenumeral l0 designates a glass electrode which is adapted to be insertedin a container II. The reference numeral 12 designates a thermionictube, the grid of which is connected to the glass electrode ii. r

The apparatus comprises a main potentiometer i3, which cooperates with amovable contact 14, and also a standardizing potentiometer 15, whichcooperates with a movable contact it. The contacts I4 and it are adaptedto be moved along their potentiometers by means of screws H and 18,respectively. These screws are driven by reversing motors I 8 and 20.

The output of the tube I2 is connected to a moving coil galvanometer 22,the coil of which carries a mirror 2|. Aiamp 23 and lens 24 direct abeam of light towards the mirror 2|. As the galvanometer coil swings,that beam of light is adapted to hit the target 25 of a photoelectriccell 26. The output of the photoelectric cell is connected to a suitableamplifier 21, which controis a relay switch 28.

The movements of the contact ll are recorded on chart 29 in a mannerwhich will be more fully described hereinafter. The movements of thecontact I! are for the purpose of standardizing the device andcorrecting changes due to loss of voltage by the cells, etc.

The potentiometer I3 is adjusted so that the movement of the contact itis adapted to the scale of the chart 23. Thus, in the case of a pHrecorder, each degree change in pH may give, for example, a voltagechange of $9 millivolts and the p tentiometer i3 should be arranged tohave a potential drop of approximately 59 millivolts for each pH spaceunit on the chart. Thus, if the potentiometer i3 is 15 inches long andwe have fourteen space units in the vertical direction on the chart 29,then we must have a potential drop of 826 millivolts on fourteen spaceunits of the potentiometer i3,

Opposite ends of the potentiometer 13 are connected to rheostatsfl and31. An operating cell 32 is connected to contact points 33 and 34 whichcooperate with the rheostats Ill and 3!, respectively. The rheostat IIIis connected to a standard cell 35 which may be connected to thegalvanometer 2| by means of the four-pole, doubleway switch 36 whenmanually thrown to the left, as viewed in Fig. 5. When thus thrown thegalvanometer is also connected to the contact 3|. The rheostai; 30 isthen adjusted to bring the galvanometer deflection to zero so that thecell 32 balances the cell 25. This may be done daily.

The galvanometer 2 2, the lamp 23 and the photoelectric cell 26 arepreferably located in a box or chamber to protect the photoelectric cell26 from extraneous light. A peep hole may be provided in this box toenable the galvanometer to be observed directly. I prefer, however, toprovide two incandescent lamps 31 and 38 which are connected by themanual switch 36 to therelay 28 which is controlled by the amplifier 21.The circuit through the lamps 31 and 38 is completed by a conductor 39which is in parallel with the lamp 23, both the circuit 39 and the lamp23 deriving energy from a transformer M which is connected to thealternating current lines.

When the switch it is turned to the left and the contact 33 is adjusted,the galvanometer 22 will be deflected until the beam of light is reilected by the mirror 2! onto the target of the photoelectric cell 25,sufliciently so that the amplifier 21 is energized and closes thecircuit through the lamp 31. The contact 33 is now moved in the oppositedirection until the lamp 38 becomes illuminated. The relaysystem may bemade so senstive that between these two o nts the ce l 32 issubstantially in balance with the cell 35. It may be noted that therelay 28 is biased towards closing towards the left, as viewed in Fig.5. Now that the working cell 32 has been standardized for the day, theswitch 35 is thrown to the right and the potentiometer II is operatedfrom cell 82. This potentiometer has previously been calibrated,preferably at the factory, by suitable movement of the contact 84 so asto bring the number of millivolts on the potentiometer I8 to the valuedesired per unit of distance, for example, centimeter or half inch,depending upon the work which the device is intended to do and the scaleof the paper which is being used.

One end of the potentiometer I8 is connected to a contact 4| whichcooperates with the potentiometer 42. This potentiometer is energized bya cell 43. It will be obvious that-manual move-.

ment of the contact 4| will cause a certain amount of displacement ofthe contact l4=when assasss of A. C. current to the set. The terminal ofthe electrode 48 is connected to a conductor III which extends throughthe cable 48 and is connected The contact 82 is connected to a conductorI2 and the conductors II and I2 are'adapted to be connected to thegalvanometer 2| when the switch 88 is thrown to the'right, as viewed inFig. 5. When the manual switch 88 is thrown to the' right, contacts 13and 14 of the single-pole double-throw switch 28 are connected to thepoles l5 and 18 respectively, of two single-pole that contactsubsequently comes to its position of balance. The purpose of thecontact 4| and potentiometer 42 is to enable the position of therecording pen 44 to be manually adjusted on the chart 29,

It maybe conveniently indicated here that when using this recorder forpH purposes, a vessel ll containing a solution of known pH is incooperative relation with the glass electrode HI. If we suppose thesolution has a pH of 7 and the pen 44 reads around 4 on the chart, thensimple manual movement of the pointer 4i will bring the pen 44 up to 7on the chart. One end of the potentiometer 42 is connected to themovable contact l6 and both are connected to a conductor 45 whichextends through a cable 48 into a housing 47 in which the thermionictube i2 is located. It may here be noted that the cable 46 may be of anydesired length and that the housing 41, the glass eiectrode i6, vesselii .and another electrode 48, which may suitably be a. KCl-calomelelectrode, are associated together as a remote unit. The glass electrodeis connected by a very short lead 69 to the grid of the tube i2. Thislead must be very short or it must be very effectively shielded in orderto avoid picking up electrical oscillations.

The housing includes relay 50 which is adapted to be energized byconductors 5i and 52 which extend through the cable 58 and are connectedto the poles 53 and 5 of a switch 55. A suitable source of energy, :Eorexample a battery 5E, may be located in the conductor 52 to providecurrent for energizing the relay Ell when the switch is closed. lhearmature 51 or" the relay is adapted, when the latter is energized, tomove into contact with the conductor 49, becoming thereby directlyconnected to the grid of the tube The armature 57 is connected to thecondoctor 55. The plate of the tube i2 is connected by a conductor toone end of a resistor 59 and one end of a manually operablepotentiometer Eli. This potentiometer is provided with a cell BI and acontact The cathode of the tube i2 is connected by a conductor 83 to thenegative side of a B battery ti t and the positive side of a C battery.The negative side of the C battery is connected to one end of thepotentiometer 15. This potentiometer is provided with a cell 86, Theheater conductors 8? of the tube 12 also pass through the cable :16 tothe control unit. The heater current is provided by a suitable battery68 and the circuit is adapted to be controlled by one of the poles of adouble-pole switch 69. The other pole of the switch 59 may control thesupply double-throw switches 11 and 18. The pole 19 of the switch 28 isconnected to terminals 88 and 8| of the two reversible motors l8 and 20.The contact 8| of the switch 11 is connected to the contact'82 of themotor IS. The contact 83 of the switch 11 is connected to the contact 84of motor 20. The contact 85 of the switch 18 is connected to the contact88 of the motor H. The contact 81 of the switch 18 is connected to thecontact 88 of the motor 28.

The poles of the switches 11, I8 and 55 are con nected together and areadapted to be operated by a relay 88. When this relay is energized, thepoles are drawn to the right as viewed in Fig. 5, pole 15 is broughtinto engagement with contact 88, pole 18 is brought into engagement withcontact 81, and pole 54 is brought into engagement with contact 53. Whenthe relay 89 is deenergized, the poles move away from these contacts andthe pole 15 makes engagement with the contact 8i and the pole 18 makesengagement with the contact 85. The relay 89 is connected to conductors80 and 8|. The conductor 90 is con- 'nected to one of the A. C. lines.The conductor 9| is connected to a switch 82 which is connected to theother 110 A. C. line. The switch 92 is suitably a mercury switch, whichis closed periodically by a cam I88.

The screw l'| is made continuous with a screw 83 of smaller pitch. Theratio of pitch between the screws H and 83 is merely a matter ofconvenience, the screw l1 carrying the contact I4 and the screw 93carrying a nut 94 which is connected by a flexible member 85 to the pen44. The nut 94 may comprise a pointer which cooperates with a fixedscale 98 so that the reading of the device at any particular time may beread directly. The chart 28 is carried on a. plate 91 which is drivencontinuously and uniformly at a slow rate of speed by means of screw 98.This screw may be driven by a synchronous clock motor 99 and the cam Hi0may suitably be mounted on its outermost end.

The physical embodiment of the invention will be more readily understoodfrom Figs. 1 to 4 inelusive. The main part of the apparatus, that is,the part represented on the left-hand side of Fig. 5, may be housed in asuitable cabinet which may comprise end frames illl secured together bysuitable bars Hi2. On one of the end frames Hi! the clock motor 89 ismounted. This motor is connected by means of gears 13 and I84 to thescrew 88. The motor 98 is driven at a constant speed from the powerlines and the screw 98 is driven at a definite speed, depending upon theunits employed. Thus, the chart 28 may be advanced at the rateof 1" perhour, /2 per hour, or one centimeter per hour, depending upon the paperemployed. The different ratios may be obaaoaass I" supported from one ofthe rods "2. The cam Ill is mounted adjacent the plate I which ispivotally mounted on the frame member. The 7 plate MB is normally heldagainst the cam III or the shaft 98 by means of a spring I01. The switch82 is carried by the plate 106. This switch is adapted to be closed fora short time only during each revolution of the shaft 88.

The plate 91 is somewhat larger than the chart 29 which isappliedthereto. The chart may be held in position on the plate- 91 byany suitable means, for example, by means of clips MI and rubber bandsI09. The plate is mounted for; easy movement in a horizontal direction.Thus, it may carry rollers I Hi near its upper edge which ride on one ofthe bars "2 to support the plate. It may also carry a roller 1 ll nearthe lower end which rides upon another of the bars I82. The plate ST mayhave an opening I through which extends ill and carries the pen Aportion of the carriage extends to the other side of the rod I. A

weight .H5 is mounted on this portion and the cord 95, which maysuitably be a silk fishing line.

The potentiometer II comprises a winding mounted upon a bar (22 ofinsulating material extending between the frame members Ill, so that thecontact it is able to engage the winding. The contact II is mounted on anut. I23 carried by the screw. The nut isprevented from rotation byprojections I which engage one of the bars ill. The contact ll causesthe potentiometer II which is wound on a bar [25 carried by the endplates ill in the same manner as the bar [22. It may here be noted thatthe screw I 8 may be much ilner than the screw II. The screw it carriesa gear I28 which is adapted to be driven by the motor 2'. when thecontacts 8i and 82 are connected together, the motor operates in onedirection and when the contacts I! and 8 are connected together, themotor operates in the opposite direction. It may here be noted thatoperation of the motor tends to bring the galvanometer 22 to null pointposition, that is, with the light reflected from the mirror 2| justhitting the target of the photoelectric cell 26.

In each case there is a certain small amount or overrunning and at theend of the short overrunning period the direction of the motor isreversed and the result is that the beam of light travels in theopposite direction. The net result is that the beam of light, under thecontrol of is attached thereto. Thecord 95 extends up wardly andslightly forwardly to a pulley H6 at the upper end of the rod ill. Thecord passes over the pulley H 5 and extends downwardly to a pulley illfrom which it extendssubstantially horizontally to the nut 34 to whichit is secured.

. one of the bars ill! to keep the nut from rotating.

The screw i1, 33 is rotatably mounted in hearings in the end plates INand a projecting end thereof carries a gear 12! which is driven by themotor i9. 7 This motor may suitably be a. reversible motorof known type,which is a single phase. shaded pole induction motor provided withshaded poles adapted, when the appropriate shading circult is completed,to operate in one direction or the other. to contact 86, a shadingcircuit is completed which causes the motor iii to move the contact I ina direction to efiect. the movement of the galvanometer beam towards thetarget of the photoelectric cell 26. When the contact III is connectedto contact 82, the motor is caused to rotate in the opposite directionand the beam of light moves away from the target of the photoelectriccell 26. When no current is passing through the galvanometer- Zi, thebeam of light reflected by the mirror 22 just hits the edge of thetarget.

either motor, has a short back and forward oscillatory movement. 0wingto the line pitch of the screw it in comparison with the screw II, thedegree of movement of the beam when operating under the control of motor2| is very small. In fact, it is so small that the position of thecontact it at any P rt of the oscillation is sufllciently accurate forpractical standardization and the fact that the motor 2| stops operatingwith the contact i iin one extreme position or in the other extremeposition, makes no practical diiference in the record.

The contact l6 and the potentiometer l5 are for the purpose ofautomatically making corrections to compensate for changes in the B bat-Thus, when contact 80 is connected tery it "C" battery 65, and so forth.The purpose of the potentimeter Cl is to .provide an adjustment wherebythe contact I may be caused to operate in approximately the middle ofthe potentiometer ii. That is. any movement of the potentiometer El willresult in the eventual displacement of the contact IS. The contact Gilprovides an electromotive'force to balance that generated by the outputof the tube i2. It is prudent to point out that when the contact 62 isdisplaced, then the next time that the switch S2 closes, the motor 20operates so as to make a corresponding translation of the point i 8towards the point of balance. If, however, the displacement of thecontact 52 is considerable, the switch S2 is closed and the beam oflight maybe deflected a very large angle from the target of thephotoelectric cell 26. The movement of the contact it tends to move thebeam of light towards the neutral point at which the beam just touchesthe target of the photoelectric cell. Eventually I the point of balanceis reached and thereafter the "contact it merely moves back and forwardslightly upon the potentiometer [5. If the displacement of the contact62 is very great, it may require several periods during which the switch92 is closed before equilibrium is attained.

The liquid in the container H should be insulated rom the ground. Inorder that I may ob-' tain. a. continuous record of the pH of a liquidrunning through a conduit M1, for example, I provide a discharge pipeI28 which terminates above the container ii and is adapted to dis chargetherei to. In pipe I28 I provide a electrically controlled valve I28.The contain Ii is provided with an overflow pipe iilil. TL: valve isconn cted to the conductors Stan 93 so that the valve 12s is opened eachme th switch 32 is closed.

This may be caused he i i on the screw Wl s opened, liquid flows frcontainer ii liq 'ne container ii so that the comt. 2 liquid in thecontainer follows e closely that of the liquid in the co duit. hen thevalve closes again there is no electrical connection between the liquidin the cont? and the ground. The container may on r be of glass and issupported on a she pended by rods of insulating materi improved devicemay be employed for con i; purposes. Thus, I may place switches 52; andin cooperative relation to the contac These switches are so locatedthatthey cl upper and lower limits of 131-1. When the ltd closes, itcompletes a circuit which corrective measures to lower the pH, for example. When the switch 533 is closed, the pH has reached its desiredminimum. This switch completes a circuit which initiates operations toraise the to a point within the desired range.

The jewel lamps 3i and 38, the potentiometers 3i, s2 and "3D, theswitches 38 and 89, and a re ceptacle i539 may be mounted on a panel litin front of the device. The receptacle I39 is intended for the receptionof a plug lei at the and number of valve 12" conduit i of the cable itfor the connection of the ixiuote unit to the main instrument.

The glass electrode it may suitably be of the common bulb type and maycomprise a platinum wire which is connected to the conductor as and dipsinto the liquid within the electrode, which may suitably consist ofdecinormal hydrochloric acid to which a small amount of quinhydrone hasbeen added. The electrode- 48 may be of the K01, HgClz-Hg type. Thiselectrode comprises a chamber I35 which contains successive layers ofmetallic mercury, mercuric chloride and saturated solution of potassiumchloride. The potassium chloride solution layer communicates through abent tube I36 into the liquid within the chamber H. The tube I36 isprovided with a stop cock I31. It is to be noted that this stop cock isnormally closed during the operation of the device. However, sufiicientliquid is present around the stop cock to maintain'electrical connectionbetween the liquid in the chamber H and the elements in chamber I35. Thconductor 10 is connected to the mercury layer by means of a platinumwire I38 which extends through the lower end of the glass chamber I35.

I prefer to connect the conductor III to the conductor 49 through acondenser I42 which may suitably be located within the housing 41. Ialso prefer to ground the conductor I0. However, the instrument willoperate satisfactorily if ungrounded and the condenser I42 be omitted.The condenser I42 may suitably have a capacity of 0.001 microfarad.

The operation of the device is as follows: The switch 69 is closed,which effects the supply of heater current to the tube I2 and powercurrent to the lamp 23, to the clock motor 89, to the motors I9 and 20,-to the amplifier 21 and, when the switch 92 is closed, as itisperiodically, to the relay 89. In the null position of thegalvanometer locate the plate :3

ubnanuellv .eiauced against the f contact viousl adjusted the particularscale 0. i;

lous'ly desc b O it'll charts 0. needs to be 11111 a we.

narlly, when opera... dimensions, no chan e respect to the contactclosed to the right. should be standardized periodically by solution.For example, a solution wt of 'i may be placed the container ii toinstrument may be allowed to function. It should give a constant readingwhich may be somewhat different than 7 and this reading may be broughtexactly to the 7 line b suit-able movement of the contact ii. The chart29 should be positioned with respect to time. This can be done, for e);-ample, by discern :ctin the plate 91 from the nut meml =3 iii and movingthis nut member back to proper position on the screw 98. Or, if desired,the screw may b disconnected from the clock motor 93 id manually turnedback to l at the proper position at the beginning line of the chart.

The automatic cper tion of the devic is then. allowed to proceed, liquidbeing admitted periodically into the tank ll from the conduit. iZ'l.This liquid displaces a corresponding amount oi liquid from the tool; Hwhich escapes through the overflow Kill. Consequently, the liquid in thechamber II is always of substantially the same composition as the liquidpassing through the conduit I27. At the beginning of the automaticoperation the contact I4 will be displaced from tors 49 and III. Thisvoltage is opposite in direction to the algebraic sum of the voltages ofthe potentiometers I3 and 42 and the voltage applied to the grid is thealgebraic sum of the voltages of the 0" battery 65, the potentiometerI5, p0- tentiometer 42, potentiometer I3, and the glass electrodesystem. Consequently, the plate current has a certain value dependingupon this algebraic sum. The resistance 59 in the plate circuit is verysubstantial, for example, of the order of 10,000 ohms. The drop ofpotential in this resistance will vary with the plate current. Thepotential across the resistance 59 is in series with the galvanometer 2|and the potentiometer 60, the voltage of which is opposite in directionto the voltage across the resistance 59.

When these two voltages neutralize each other, the galvanometer 2I is inits null or neutral positlon. If one is greater than the other, thegalvanometer is displaced and the direction of its displacement controlsthe switch 28, with the result that the motor I9 is operated in onedirection or the other. The direction of operation of the motor I9effects a movement of the contact I I, which changes the effectivevoltage in the grid circuit provided by the potentiometer I3.

The plate current is consequently changed and the voltage drop acrossthe resistance BI is correspondlngly altered in a direction which tendsto bring it into equality with the voltage oi the potentiometer 80. Thatis, the operation of the motor i8 is always in the direction tending tobring the beam of light to a point where it Just touches the target oithe photoelectric cell 28.

If it is assumed that the beam was initially oil the target and that themotor I! is moving the contact H in the appropriate direction, then thebeam of light will hit the target and the switch 28 will change over soas to reverse the direction of rotation of the motor It. It is to benoted that the motor will overrun slightly before it reverses. Thereversal oi. the motor effects a reverse change of the contact i4 andthe result is that the grid circuit will vary and the plate circuit willvary so that the beam moves off the target again. Again it overrunsbefore the reversal of the motor it becomes eilective. The result isthat the pen will oscillate up and down, producing a stout line, as bestseen in Fig. 1. For convenience, I read the top of this thick line onthe chart and I consider the top of this line when adjusting the readingwith the aid of a buffer solution. It will readily beunderstood that anyvariation of the pH of the liquid in the container ii will create achange of grid voltage and a change oi. plate voltage which will havethe eilect of necessitating a changed position of remains set duringoperation, the potentiometer it necessarily varies in accordance withthe variation of the voltage created by the glass electrode and hencethe line drawn by the pen I accurately depicts changes or voltagecreated by the glass electrode and, consequently, the pH of the solutionin the tank H for the time being. 7

During the operation of the device the pH of the liquid in the chamber Hmay be read directly by the scale 8|. As has been hereinb'efore pointedout, mechanical means, for example, switches (33 and I34, may beassociated with the contact i4 so that they may initiate-or controlcorrective measures in case the pH of the liquid tends to deviate beyondcertain predetermined limits.

Although the invention has been disclosed in connection with thespecific details of a preferred embodiment thereof, it must beunderstood that such details are not intended to be limitative of theinvention except in so far as set iorth in the accompanying claims.

Having thus described my invention. what I claim as new and desire tosecure by Letters Patent of the United States is:

1. An automatic recorder comprising a recording pen, continuouslyoperating driving means adapted to move said pen in opposite directions,

electrical means associated with the penprogresthe contact M in order tokeep the galvanometer oscillating at its zero position. That is, if thepH of the liquid'increases, the oscillating position of the pen M willbecome elevated and vice versa.

During the normal operation the cam or cams I00 momentarily closes theswitch 92 at regular intervals. The closing of the switch effects theopening of the valve I25 and the supply of a certain amount of liquid tothe chamber ii. The closing of this switch also results in theenergization of the relay 89 and the throwing of the switch 71 to theright, as viewed in Fig. 5. When the contacts 53 and 54 come intoengagement, the relay 5!) is energized and the contact 5'! is connecteddirectly to the grid. The contact 51 being connected directly to thecontact [6, the potentiometers l3 and 2 and the glass electrode are cutout of the grid circuit and only the C battery 65 and the potentiometerremain effective.

The galvanometer is now subjected to the plate current which resultsfrom the voltage of the 0" battery and the potentiometer it. The relay89 being energized and the switch 1T being moved to its right-handposition, as viewed in Fig. 5, the switch 28 is connected to the motorinstead of the motor i9 and consequently the pointer l6 moves to aposition of balance and then oscillates at that balance. Owing to thefact that the screw i8 is much finer than the screw H, the oscillationsmade by the contact [6 are much smaller than those made by the contactH. The result is that any position of the contact it within itsoscillating ambit is suillciently accurate for the purpose ofstandardizing the circuits. When the switch 92 opens again, the contacti6 is left in the standardized position, the motor is is now renderedoperative and the potentiometers l3 and 42 and the glass electrode areagain introduced into the grid circuit. Consequently, when oscillatingbalance of the pen is obtained, the voltage created by the glasselectrode exactly counter-balances the voltages introduced by thepotentiometers l3 and 42. Since the potentiometer 42 sively changed withmovements of the pen in opposite directions, and relay means controlledby said electrical means for reversing the driving means, said relaymeans being biased to cause' movement of the pen in one direction andbeing adapted to be actuated by said electrical means to cause movementof the pen in the opposite direction.

2. An automatic recorder comprising a pen, continuously operatingdriving means for operating said pen in alternating directions, anelectric circuit including means providing a voltage to be recorded andmeans for supplying voltage variable in accordance with the change ofposition of said pen, and relay means responsive to the sum of saidvoltages for reversing the driving means, said relay means being biasedto cause movement of the pen in one direction and being responsive tosaid sum or" the voltages, when sufiiciently great, to cause movement ofthe pen in the opposite direction.

-3.'A'n automatic recorder comprising a pen, continuously operatingdriving means for operating said pen in alternating directions, anelectric circuit including means providing a voltage to be recorded andmeans for supplying voltage variable in accordance with the change ofposition of said pen, a single photoelectric cell controlled by thejoint action of said voltages, and relay means controlled by saidphotoelectric cell ior reversing the driving means, said relay meansbeing biased to cause movement of the pen in one direction and beingadapted to be energized by said photoelectric cell to cause movement ofthe pen in the opposite direction.

4. In an automatic recorder, a galvanometer adapted to project a beam oflight, a reversing driven member adapted continuously to change thecurrent flowing through the galvanometer, a photoelectric cell adaptedto be impinged by said beam in one position of the galvanometer, a relaybiased to cause said'driven member to move in a direction to bring thebeam towards the photoelectric cell and adapted "to be energized by thephotoelectric cell to reverse the driven member continuously, meansproviding an electrical eilect to be measured tending to change thecurrent flowing through the galvanometer, and means maintaining thegalvanometer current within a substantially constant range.

5. An automatic recorder comprising a moving chart, a pen cooperatingtherewith, a reversible motor adapted to move said pen in opposite d1rections, a potentiometer controlled by said mo tor correlation with thepen movements provide a voltage, means for providing a variable voltageto be measured in series with the potentiometer, a gelvanometercontrolled by said voltages, and relay means controlled by saidgaivanometer and controlling the directionoi' the motor, wherebymovements of the galvanometer in one direction immediately actuate therelay means to effect reversal of the galvanometer movement, whereby thegalvanometer is main tained in a state of continuous oscillation withinclose limits.

d-An automatic recorder comprising a moving chart, a pen cooperatingtherewith, a reversible motor adapted to move said pen in oppositedirections, a potentiometer controlled by said motor in correlation withthe pen movements, means for providing a variable voltage to be measuredin series with the potentiometer, a galvanometer controlled by saidvoltage and the voltage of the potentiometer, a photocell adapted tobe'energized by said galvanometer, and relay means biased to control theactuation of the motor in one direction and adapted to be energized bysaid photocell for reversing the motor thereby causing the galvanometerto swing continuously within close limits.

7. An automatic recorder comprising a moving chart, a pen cooperatingtherewith, a continuously operating motor adapted to move said pen inopposite directions, a. thermionic tube having a grid circuit and aplate circuit, a. potentiometer controlled by said motor in correlationwith the pen movements and means for providing a variable voltage to bemeasured in series in the grid circuit. a galvanometer in the platecircuit, and relay means adapted to reverse the motor repeatedly as thegalvanometer swings within close limits.

8. An automatic recorder comprising a moving chart, a pen cooperatingtherewith, a reversible motor adapted to move said pen in oppositedirections, a potentiometer controlled by said motor in correlation withthe pen movements to provide a voltage, a, second potentiometer inseries with first said potentiometer to provide a voltage, a secondreversible motor controlling last said potentiometer, means providing a.variable voltage to be measured in series with the potentiometers, agalvanometer controlled by said voltages, relay means adapted to reversethe" first said motor repeatedly during its period of operation War:

lit

as galvanometer swings within close limits, and periodically operableswitching means for out ng out the first said potentiometer and themeans providing the variable voltage to be measured and for connectingthe relay means to the second motor whereby the second motor is reversedrepeatedly during its period oi operation and the galvanometer is causedto swing in close limits at substantially the same position.

9. An automatic recorder comprising a moving chart, a pen cooperatingtherewith, a reversible motor adapted to move said pen in oppositedirections, a thermionic tube having a grid circuit and a plate circuit,a potentiometer in the grid circuit controlled by said motor incorrelation with the pen movements, at second potentiometer and meansfor providing a variable voltage to be measured in said grid circuit, asecond reversible motor controlling said second potentiometer, a

galvanometer in the plate circuit, relay means adapted to reverse thefirst said motor repeatedly during its period of operation as thegalvanometer swings between close limits, and automatic switching meansoperable periodically to cut out the first said potentiometer and themeans providing the variable voltage to be measured and for connectingthe relay means to the second motor whereby the second motor is reversedrepeatedly during its period of operation and the galvanometer is causedto swing in close limits at substantially the same position.

10. An automatic recorder comprising a moving chart, a-pen cooperatingtherewith, a reversible motor adapted to move said pen in oppositedirections, a thermionic tube having a grid circult and a plate circuit,a potentiometer in the grid circuit controlled by said motor incorrelation with the pen movements, a second potentlometer and hydrogenion responsive means for providing a variable voltage to be measured insaid grid circuit, a second reversible motor controlling said secondpotentiometer, means for supplying fluid to be tested in said hydrogenion responsive means, a. galvanometer in said plate circuit, a. photocell adapted to be energized by said galvanometer, an amplifierconnected to said photocell, a relay controlled by said amplifier toreverse the first said motor repeatedly during its period of operationas the galvanometer swings between close limits, and automatic switchingmeans for periodically actuating said fiuid supply means and cutting outthe first said potentiometer and the hydrogen ion voltage and iorconnecting the relay to the second motor whereby the second motor isreversed repeatedly during its period of operation and the galvanometeris caused to swing in close limits at substantially the same position.

DONALD H. CAMERON.

